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Discus (fish)
Symphysodon (colloquially known as discus or discus fish) is a genus of cichlids native to the Amazon river basin in Brazil. Due to their distinctive shape, calm behavior, many bright colors and patterns, and dedicated parenting techniques, discus are popular as freshwater aquarium fish, and their aquaculture in several countries in Asia (notably Thailand) is a major industry. They are sometimes referred to as pompadour fish. The discus fish has attracted a cult following of collectors and has created a multimillion dollar international industry complete with shows, competitions, and reputable online breeders[citation needed].
The genus name "symphysodon", which was coined in 1840 by Johann Jakob Heckel, refers to the unusual symphysis of the teeth (-odon from Greek ὀδών, tooth).
Following a review published in 2006, three species are recognized by FishBase:
Discus are fish from the genus Symphysodon, which currently includes the species S. aequifasciatus, S. discus and S. tarzoo, based on a taxonomic review published in 2006. A review published in 2007 largely came to the same result, but differed in nomenclature, as the species called S. tarzoo in the 2006 study was called S. aequifasciatus in the 2007 study, and S. aequifasciatus in 2006 was S. haraldi in 2007. Further arguments have been made that S. tarzoo was not described in accordance with ICZN rules and thus should be considered invalid and replaced with S. haraldi, currently considered a synonym of S. aequifasciatus by FishBase.
Other species and subspecies have been proposed, but morphometric data (unlike in Pterophyllum, the freshwater angelfish) varies as much between individuals from one location as across the whole range of all discus fish species.[citation needed] S. tarzoo was described in 1959 and applies to the red-spotted western population. S. aequifasciatus and S. discus, meanwhile, seem to hybridise frequently in the wild or have diverged recently, as they lack mitochondrial DNA lineage sorting but differ in color pattern and have dissimilar chromosomal translocation patterns. S. discus occurs mainly in the Rio Negro. Whether S. haraldi is indeed distinct from S. aequifasciatus remains to be determined; if valid it is widespread but it might just be a color morph.[citation needed]
A molecular study in 2011 found five main groups, which generally matched previously recognized phenotypes. They recognized them as evolutionarily significant units and species. Their assigning of scientific names to species differed to some extent from that used by earlier authors: Heckel (S. discus; Rio Negro, upper Uatumã, Nhamundá, Trombetas and Abacaxis), green (S. tarzoo; West Amazon drainages upriver from the Purus Arch, blue (S. sp. 1; central Amazon from Purus Arch to the Meeting of Waters), brown (S. aequifasciatus; East Amazon downriver from Meeting of Waters), Xingu group (S. sp. 2; Xingu and Tocantins). The Xingu group currently lacks a scientific name, but it is possible that the correct name for the blue is S. haraldi. This taxonomy with four described valid species, S. discus, S. tarzoo, S. haraldi and S. aequifasciatus, has been adopted by the Catalog of Fishes. Some hybridisation occurs (or has occurred) between the brown discus and neighbouring forms, but overall they maintain their separate evolutionary trajectories.
In addition to the wild discus, several captive variants achieved by selective breeding exist. Based on RAPD sequences, the captive variants popularly known as turquoise, pigeon, ghost, cobalt and solid red are derived from wild green, blue and brown discus (not Heckel discus).
Like cichlids from the genus Pterophyllum (angelfish), all Symphysodon species have a laterally compressed body shape. In contrast to Pterophyllum, however, extended finnage is absent giving Symphysodon a more rounded shape. It is this body shape from which their common name, "discus", is derived. The sides of the fish are frequently patterned in shades of green, red, brown, and blue. Some of the more brightly marked variants are the result of selective breeding by aquarists and do not exist in the wild. Discus typically reach up to 12.3–15.2 cm (4.8–6.0 in) in length, but captives have been claimed to reach 23 cm (9 in). Adults generally weigh 150–250 g (5.3–8.8 oz). Discus fish exhibit no sexual dimorphism when they are under about 4 inches in size, making it difficult to distinguish between males and females at a young age. Once they reach this size, the shape of their dorsal fins begins to change, with females retaining rounder dorsal fins and males developing more pointed ones. Other subtle indicators of sex include the overall size, as males are usually larger, and the thickness of their lips, with males often having thicker lips used for fighting. Despite these clues, none of these characteristics are guaranteed indicators of sex. The only definitive way to confirm the sex of discus fish is by observing spawning behavior, where a female lays eggs and a male swims over to fertilize them.[citation needed]
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Discus (fish)
Symphysodon (colloquially known as discus or discus fish) is a genus of cichlids native to the Amazon river basin in Brazil. Due to their distinctive shape, calm behavior, many bright colors and patterns, and dedicated parenting techniques, discus are popular as freshwater aquarium fish, and their aquaculture in several countries in Asia (notably Thailand) is a major industry. They are sometimes referred to as pompadour fish. The discus fish has attracted a cult following of collectors and has created a multimillion dollar international industry complete with shows, competitions, and reputable online breeders[citation needed].
The genus name "symphysodon", which was coined in 1840 by Johann Jakob Heckel, refers to the unusual symphysis of the teeth (-odon from Greek ὀδών, tooth).
Following a review published in 2006, three species are recognized by FishBase:
Discus are fish from the genus Symphysodon, which currently includes the species S. aequifasciatus, S. discus and S. tarzoo, based on a taxonomic review published in 2006. A review published in 2007 largely came to the same result, but differed in nomenclature, as the species called S. tarzoo in the 2006 study was called S. aequifasciatus in the 2007 study, and S. aequifasciatus in 2006 was S. haraldi in 2007. Further arguments have been made that S. tarzoo was not described in accordance with ICZN rules and thus should be considered invalid and replaced with S. haraldi, currently considered a synonym of S. aequifasciatus by FishBase.
Other species and subspecies have been proposed, but morphometric data (unlike in Pterophyllum, the freshwater angelfish) varies as much between individuals from one location as across the whole range of all discus fish species.[citation needed] S. tarzoo was described in 1959 and applies to the red-spotted western population. S. aequifasciatus and S. discus, meanwhile, seem to hybridise frequently in the wild or have diverged recently, as they lack mitochondrial DNA lineage sorting but differ in color pattern and have dissimilar chromosomal translocation patterns. S. discus occurs mainly in the Rio Negro. Whether S. haraldi is indeed distinct from S. aequifasciatus remains to be determined; if valid it is widespread but it might just be a color morph.[citation needed]
A molecular study in 2011 found five main groups, which generally matched previously recognized phenotypes. They recognized them as evolutionarily significant units and species. Their assigning of scientific names to species differed to some extent from that used by earlier authors: Heckel (S. discus; Rio Negro, upper Uatumã, Nhamundá, Trombetas and Abacaxis), green (S. tarzoo; West Amazon drainages upriver from the Purus Arch, blue (S. sp. 1; central Amazon from Purus Arch to the Meeting of Waters), brown (S. aequifasciatus; East Amazon downriver from Meeting of Waters), Xingu group (S. sp. 2; Xingu and Tocantins). The Xingu group currently lacks a scientific name, but it is possible that the correct name for the blue is S. haraldi. This taxonomy with four described valid species, S. discus, S. tarzoo, S. haraldi and S. aequifasciatus, has been adopted by the Catalog of Fishes. Some hybridisation occurs (or has occurred) between the brown discus and neighbouring forms, but overall they maintain their separate evolutionary trajectories.
In addition to the wild discus, several captive variants achieved by selective breeding exist. Based on RAPD sequences, the captive variants popularly known as turquoise, pigeon, ghost, cobalt and solid red are derived from wild green, blue and brown discus (not Heckel discus).
Like cichlids from the genus Pterophyllum (angelfish), all Symphysodon species have a laterally compressed body shape. In contrast to Pterophyllum, however, extended finnage is absent giving Symphysodon a more rounded shape. It is this body shape from which their common name, "discus", is derived. The sides of the fish are frequently patterned in shades of green, red, brown, and blue. Some of the more brightly marked variants are the result of selective breeding by aquarists and do not exist in the wild. Discus typically reach up to 12.3–15.2 cm (4.8–6.0 in) in length, but captives have been claimed to reach 23 cm (9 in). Adults generally weigh 150–250 g (5.3–8.8 oz). Discus fish exhibit no sexual dimorphism when they are under about 4 inches in size, making it difficult to distinguish between males and females at a young age. Once they reach this size, the shape of their dorsal fins begins to change, with females retaining rounder dorsal fins and males developing more pointed ones. Other subtle indicators of sex include the overall size, as males are usually larger, and the thickness of their lips, with males often having thicker lips used for fighting. Despite these clues, none of these characteristics are guaranteed indicators of sex. The only definitive way to confirm the sex of discus fish is by observing spawning behavior, where a female lays eggs and a male swims over to fertilize them.[citation needed]
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